Battery packs for electric and/or hybrid vehicles typically include one or more high voltage batteries to provide the energy required by the drive systems of such vehicles. Such high voltage batteries typically provide voltages of above 100 volts (V), for example, up to 400 V. Some battery packs include a high voltage cutoff system comprising a high voltage contactor for disconnecting the high voltage battery in certain circumstances. A high voltage contactor is an electrically controlled switch capable of switching a high power circuit, such as, for example, a circuit operating at more than 15 amperes (A). However, this single contactor system has some drawbacks. For example, certain fault conditions, such as a high voltage short-circuit, can cause the contactor to weld to metal portions of the battery circuit. Specifically, the fault condition can cause an electrical arc to form across the contactor, causing metal portions of the contactor to heat to a very high temperature (e.g., high enough to form a plasma). If the heated portions of the contactor come into contact with each other, and remain in contact while cooling down, the contactor portions bond together to create a solid connection across the contactor and therefore, between the high voltage battery and the battery circuit.
In view of this, some automotive manufacturers have implemented a dual-contactor system comprising a redundant second contactor that is intended to disconnect the high voltage battery in the event of a welded first contactor. As an example, FIG. 1 depicts a conventional dual-contactor system 100 found in some commercially-available electric and/or hybrid vehicles. The dual-contactor system 100 includes a battery module 102 coupled to a vehicle bus 104 (also referred to as a high voltage bus) via two leads, DCL+ and DCL−. The battery module 102 includes a high voltage battery 106 with two leads MC+ and MC−, and two contactors 108 and 110. The contactor 108 selectively couples the MC+ lead to the DCL+ lead, while the contactor 110 selectively couples the MC− lead to the DCL− lead. During normal operation of the vehicle (e.g., while the vehicle is being driven), the contactors 108 and 110 are in a closed position, so that the high voltage battery 106 is electrically coupled to the vehicle bus 104. In the event of a vehicular impact or other fault condition, the contactors 108 and 110 are switched open in order to disconnect the high voltage battery 106 from the vehicle bus 104.
As shown in FIG. 1, the dual-contactor system 100 can also be used in Plug-in Hybrid Electric Vehicles (PHEV) and Battery Electric Vehicles (BEV) where a vehicle charger 112 can supply power to the vehicle bus 104. In such cases, the battery module 102 includes contactors 109 and 111 for selectively coupling the vehicle charger 112 to the DCL+ and DCL− leads, respectively, and disconnecting the vehicle charger 112 from the vehicle bus 104 upon impact.
Further, as shown in FIG. 1, the battery module 102 can include a precharge circuit 113 that can also include a contactor 115. The battery module 102 may have a specific contactor closing sequence in order to eliminate the potential for arcing when turning on the vehicle. For example, in the battery module 102, the contactor 108, which is coupled to the positive lead MC+ of the high voltage battery 106, may be closed first, then the precharge contactor 115 may be closed, and lastly, the contactor 110, which is coupled to the negative lead MC− of the high voltage battery 106, may be closed. Once the vehicle is turned on, the precharge contactor 115 may be switched open, but the other two contactors 108, 110 may remain closed while the vehicle is being driven. As a result, when an accident or collision occurs, the precharge contactor 115 is already in an opened state and therefore, may not be affected by the above-described potential for arcing and welding.